Traffic accidents which endanger the occupants of a vehicle, such as, for instance, impact of the vehicle against a stationary obstacle or collision with another vehicle, is an occurrence which proceeds extremely rapidly and lasts for only about 100 milliseconds from the first contact with the obstacle until its end. On the other hand, protective means for protecting the occupants from injury in an accident, such as safety belts and/or airbags, require a certain minimum amount of time for their activation. By activation, there is understood, for instance, in the case of an airbag, the procedure which extends from the igniting of the gas injection charge until the airbag has been inflated into its protective position. For this, a few dozen milliseconds are required. In the protective systems described above there is therefore the problem, in particular, of noting the potential for endangerment in an accident as early as possible in order to be able to activate the protective system provided in the vehicle so rapidly that, taking into account the time for its activation, it can still contribute to protecting the occupant. For example, an airbag must be inflated sufficiently early that the occupant who is greatly accelerated by the forces occurring upon the accident does not strike his head on parts of the vehicle, for instance the steering wheel, and thereby seriously injure himself. On the other hand, the triggering mechanism for the protective system must not be so sensitive that it responds and activates the protective system at values of acceleration which are not dangerous for the occupants. This would namely result in a high expense for the repair of the unnecessarily activated protective system.
There have been numerous attempts to solve this difficult problem. Thus, a protective device is known from U.S. Pat. No. 4,020,453 which has an acceleration sensor which notes the acceleration of the vehicle and in which the acceleration signal is integrated and the protective system triggered when the integrated acceleration value has exceeded a threshold value which can be preset. In this known safety device therefore, an integrated acceleration value can be preset by a threshold value which is considered so dangerous that the activating of the protective system is then necessary. This known safety device disregards the position in which the occupant to be protected is actually sitting, and which may differ greatly from case to case. For example, the occupant may be sitting with his back pressed firmly against the backrest of the car seat or he may have his head in the vicinity of the instrument panel in order, for instance, better to read a display. However, the optimal protective action of the protective system depends on the position in which the passenger in the vehicle is actually sitting.
Therefore, attempts have also been made to note the actual position of the passenger and take it into account for activation of the protective system. Such protective systems are known, for instance, from Germany Patent Application Nos. DE 40 05 598 A1, DE 38 09 074 A1 and DE 40 23 109 A1. These last-mentioned solutions are, however, comparatively expensive since they require additional sensors such as, for instance, seat contacts, ultrasonic barriers, light barriers or the like, in order to note the actual position of the passenger. The application of such additional sensors and evaluation means for them to different vehicles, and possibly also their adaptation to the different shape of occupants of the vehicle, means a large expense for construction and maintenance. Finally, these additional components may also, as a whole, impair the reliability of the protective system, since defects can occur in the wires and contact means necessary for the connecting of the sensors and evaluation units.
In accordance with a further solution of the problem described above, it has, it is true, been attempted, in accordance with Germany Patent Application No. DE 38 03 426 A1, to take the actual position in which the occupant of the car is sitting into consideration in connection with the activating of the protective system. In accordance with this known solution, however, the actual position in which the occupant is sitting is no longer noted by sensors, but it is attempted to calculate the forward displacement of the occupant which occurs as a result of acceleration by means of the acceleration of the vehicle noted by an acceleration sensor on the basis of a mathematical formula. For the use of this formula, the occupant is considered to be a freely movable mass with respect to the vehicle. Further influences, such as, for instance, the supporting of the driver on the steering wheel, the spring action of the vehicle seats and the like, can be taken into account in the manner that corresponding correction factors describe the forward displacement of the occupant in the manner of a massspring system.
Proceeding from this known prior art, the object of the present invention is to improve the triggering of a protective system for the occupants of vehicles by also taking into account the actual position in which the occupant is sitting.